Remove and finely chop the mushroom stems. Set aside. Using a spoon, scrape out the gills (the black part on the underside of the mushroom cap) and discard. Set aside.
In a large bowl combine all the marinade ingredients. Add the mushroom caps and coat well. Marinate for about 10 minutes.
With the rack in the middle position, preheat the oven 400°F. Line a baking sheet with aluminum foil or parchment paper.
In a skillet over medium heat add the chopped mushroom stems, bell pepper, and onion. Season with salt and pepper. Sauté over medium-high heat for about 2 minutes. Add the spinach, broth, and wine. Bring to a boil and reduce until almost dry.
Remove the mushroom caps from the marinade and arrange them on the baking sheet. Season with salt and pepper. Fill with the stuffing and sprinkle with the cheese. Roast until the cheese is lightly browned, about 30 minutes.
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